The increasing use of chain saws has resulted in an increasing number of chain saw accidents, many of which are extremely serious. One of the primary causes of accidents involving chain saws is the problem of chain saw kickback. Kickback usually occurs when the chain first engages the object to be cut and can cause the saw to fly out of control, often rotating in the air and striking the user while the blade is still in motion.
Many chain saws now include safety devices such as chain brakes which are intended to operate when kickback occurs. However, the operating mechanisms for such devices often become clogged with saw dust preventing proper operation and the brake mechanisms involved may not be properly serviced thereby resulting in operational failures in use. Certainly, the increasing incidence of chain saw accidents would seem to indicate that such mechanisms have not been entirely effective.
Other forms of safety devices have also been proposed over the years including that shown in U.S. Pat. No. 4335513 Owens. This patent describes a bar which is pivotted to the handle of the chain saw to overlie the top run of the chain at a fixed spacing therefrom to avoid contact between the chain and the bar. While the concept behind the safety bar described in this patent is commendable, the device has never been commercialized and suffers from a number of disadvantages. Firstly, the device is only suitable for "in line" chain saw handles, that is, where the handle is situated in alignment with the cutter bar of the saw, and such chain saws are quite rare. Secondly, the mounting of the safety bar on the handle of the chain saw prevents the use of the device with chain saws having chain brakes or anti-vibration devices fitted thereto, since such devices occupy the space in which the safety bar is intended to be positioned. Thirdly, the mounting of the safety bar on the handle of an existing chain saw would severely weaken the strength of the handle so that the device is really only suitable for use with a handle which is has been specifically manufactured with a mounting fitting adapted to accept the pivot mechanism for the safety bar. Fourthly, the device must be manually pivotted to enable boring or undercut operations to be performed and since this reduces the control which the operator has over the saw, such an operation is regarded as being potentially dangerous.